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Hello dear RPi friends,

an HDMI cable is connected to an audio extractor at HDMI 0 (near USB-C) to tap off the audio signal for further output. No video signal is used by the audio extractor.

/boot/config.txt:

# uncomment if hdmi display is not detected and composite is being output
hdmi_force_hotplug=1

uncomment to force a specific HDMI mode (this will force VGA)


#hdmi_group=1
#hdmi_mode=1


uncomment to force a HDMI mode rather than DVI. This can make audio work in


DMT (computer monitor) modes


hdmi_drive=2
...

aplay -l:

Karte 0: b1 [bcm2835 HDMI 1], Gerät 0: bcm2835 HDMI 1 [bcm2835 HDMI 1]
  Sub-Geräte: 4/4
  Sub-Gerät #0: subdevice #0
  Sub-Gerät #1: subdevice #1
  Sub-Gerät #2: subdevice #2
  Sub-Gerät #3: subdevice #3
Karte 1: Headphones [bcm2835 Headphones], Gerät 0: bcm2835 Headphones [bcm2835 Headphones]
  Sub-Geräte: 4/4
  Sub-Gerät #0: subdevice #0
  Sub-Gerät #1: subdevice #1
  Sub-Gerät #2: subdevice #2
  Sub-Gerät #3: subdevice #3

If you need any more information, just write. I'm grateful for every solution or hint how to force or display hdmi 0 to get my audio signal over it.

Greetings from germany!

cheat.008
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1 Answers1

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The Pi4 (in contrast to earlier models) has NO video output unless a monitor is detected. See https://www.raspberrypi.com/documentation/computers/config_txt.html#hdmi-mode

The OS CAN be forced to set resolution even if no monitor is detected.

You don't say which OS but Bullseye adds additional limitations. See What are the pros and cons of the new Raspberry Pi OS Bullseye?

The setting you list don't work with kms driver. See https://www.raspberrypi.com/documentation/computers/configuration.html#fake-or-full-kms-graphics-driver

I have enabled the in-built VNC server to use headless (which disables Mutter, although I can't detect any difference).

Milliways
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